In order to efficiently perform a data communication, there is a technology for measuring a communication bandwidth (hereinafter, referred to just as bandwidth) indicating a transmission rate that is usable in the data communication and for transmitting data in accordance with the measured bandwidth in a communication device such as a router for relaying communications (for example, see Patent Literature 1). By utilizing such technology, such communication device may measure a usable bandwidth in advance and perform a control so that data may not be transmitted beyond the usable bandwidth, thereby reducing packet loss in the communication network.